misc: use collections.abc to import ABCs from.

Squelches remaining warnings of this type:

DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working

rlp/codec.py

@@ -77,7 +77,7 @@ def encode_raw(item):
             return item
         payload = item
         prefix_offset = 128  # string
-    elif not isinstance(item, str) and isinstance(item, collections.Sequence):
+    elif not isinstance(item, str) and isinstance(item, collections.abc.Sequence):
         payload = b''.join(encode_raw(x) for x in item)
         prefix_offset = 192  # list
     else:
@@ -274,7 +274,7 @@ def infer_sedes(obj):
         return big_endian_int
     elif BinaryClass.is_valid_type(obj):
         return binary
-    elif not isinstance(obj, str) and isinstance(obj, collections.Sequence):
+    elif not isinstance(obj, str) and isinstance(obj, collections.abc.Sequence):
         return List(map(infer_sedes, obj))
     elif isinstance(obj, bool):
         return boolean

rlp/sedes/lists.py

@@ -1,7 +1,7 @@
 """
 Module for sedes objects that use lists as serialization format.
 """
-from collections import Sequence
+from collections.abc import Sequence
 
 from eth_utils import (
     to_list,

rlp/sedes/serializable.py

@@ -186,7 +186,7 @@ def Changeset(obj, changes):
     return cls(obj, changes)
 
 
-class BaseSerializable(collections.Sequence):
+class BaseSerializable(collections.abc.Sequence):
     def __init__(self, *args, **kwargs):
         if kwargs:
             field_values = merge_kwargs_to_args(args, kwargs, self._meta.field_names)

tests/test_lazy.py

@@ -1,4 +1,4 @@
-from collections import Sequence
+from collections.abc import Sequence
 
 import pytest